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jeremybenn |
Target Definitions for R8C/M16C/M32C
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Copyright (C) 2005, 2007
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Free Software Foundation, Inc.
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Contributed by Red Hat.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published
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by the Free Software Foundation; either version 3, or (at your
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option) any later version.
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GCC is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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License for more details.
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You should have received a copy of the GNU General Public License
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along with GCC; see the file COPYING3. If not see
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.
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These are just some random notes I used during development of this
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port. Please don't consider these to be "official" specifications,
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just additional information to help make the code easier to
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understand.
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Frame
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=====
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+--------------------
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| incoming args
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+--------------------
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| return Address
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osp -> +--------------------
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| saved fp
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fp -> +--------------------
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| local data
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+--------------------
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| saved regs
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+--------------------
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| outgoing args (opt)
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sp -> +--------------------
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Argument Passing
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================
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r8c, m16c
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---------
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First arg may be passed in r1l or r1 if it (1) fits (QImode or
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HImode), (2) is named, and (3) is an integer or pointer type (no
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structs, floats, etc). Otherwise, it's passed on the stack.
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Second arg may be passed in r2, same restrictions (but not QImode),
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even if the first arg is passed on the stack.
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Third and further args are passed on the stack. No padding is used,
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stack "alignment" is 8 bits.
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m32cm, m32c
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-----------
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First arg may be passed in r0l or r0, same restrictions as above.
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Second and further args are passed on the stack. Padding is used
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after QImode parameters (i.e. lower-addressed byte is the value,
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higher-addressed byte is the padding), stack "alignment" is 16 bits.
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Return Value
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============
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r8c, m16c
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---------
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QImode in r0l
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HImode in r0
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near pointer in r0
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(desired)
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SImode in r2r0
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far pointer in r2r0
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(actual)
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Anything bigger than 16 bits is returned in memory, at mem0 (mem0
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through mem15 are provided by libgcc.a)
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Aggregate values (regardless of size) are returned by pushing a
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pointer to a temporary area on the stack after the args are pushed.
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The function fills in this area with the value. Note that this
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pointer on the stack does not affect how register arguments, if any,
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are configured.
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m32cm, m32c
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-----------
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Same.
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Registers Preserved Across Calls
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================================
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r8c, m16c
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---------
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sb, fb, sp (i.e. nearly all registers are call clobbered)
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m32cm, m32c
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-----------
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r1, r2, r3, a0, a1, sb, fb, sp
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(except when used for return values)
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Interrupt Handlers
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==================
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The stack frame is slightly different for interrupt handlers, because
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(1) we don't have a usable parent frame, and (2) we have to use
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special instructions to return and thus must save/restore everything
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differently.
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+--------------------
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| program state
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osp -> +--------------------
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| return address
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+--------------------
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| saved r0..fp (pushm)
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fp -> +--------------------
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| local data
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+--------------------
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| saved regs mem0..mem15
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+--------------------
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| outgoing args (opt)
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sp -> +--------------------
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